Qianjiangsaurus (meaning "Qianjiang lizard") is an extinct genus of hadrosauroidean ornithopod dinosaurs from the Late Cretaceous Zhengyang Formation of China. The genus contains a single species, Q. changshengi, known from a partial skeleton. Qianjiangsaurus is one of the few hadrosauroids named from south China, and it indicates important fauna connections between similarly aged formations in Mongolia.

The Qianjiangsaurus holotype specimen, CLGRP V00016, was discovered by a paleontological expedition associated with the Chongqing Bureau of Geological and Mineral Resource Exploration and Development during the winter of 2022. The locality represents sediments of the Zhengyang Formation near Zhengyang area in Qianjiang District, Chongqing Municipality of southwest China. The specimen consists of a partial, somewhat articulated skeleton, comprising an incomplete mandible, four dorsal vertebrae, the sacrum, many caudal vertebrae and associated chevrons, most of the pelvic girdle, and several hindlimb bones.

After being announced in August 2024 in a non-finalized preprint, Dai et al. (2025) described Qianjiangsaurus changshengi as a new genus and species of hadrosauroid dinosaurs based on these fossil remains. The generic name, Qianjiangsaurus, combines "Qianjiang"—the name of the district containing the type locality—with the Greek σαῦρος (sauros), meaning 'lizard'. The specific name, changshengi, Changsheng Wang, the discoverer of the Chongqing fossil locality.

Nanningosaurus, a genus from the Nalong Basin of Guangxi, is the only other hadrosauroid currently named from south China.

The holotype of Qianjiangsaurus likely represents a mature adult individual. It is medium-sized in comparison to related taxa, at about 8 metres (26 ft) long.

The prepubic process of the pubis is fan-shaped, with a length:height ratio of about 0.79, representing the single autapomorphy (unique derived trait) identified in the holotype. The unique combination of other characters includes a total of 30 dentary tooth positions with no more than five teeth per alveolus (tooth socket), a coronoid process at a right angle to the dentary, and seven fused vertebrae in the sacrum. While some of its plesiomorphic (ancestral) anatomical features confidently place it within the Hadrosauroidea, it still demonstrates apomorphic (derived) features of later-diverging members of the Hadrosauridae, placing it as a transitional form between the two groups.

In their phylogenetic analyses, Dai et al. (2025) recovered Qianjiangsaurus as the sister taxon to the Mongolian Plesiohadros, with these taxa as late-diverging members of the Hadrosauroidea outside of the Hadrosauridae. Their results are displayed in the cladogram below:

The discovery of Qianjiangsaurus provides further support for several faunal similarities between the Zhengyang Formation of China and the Djadokhta and Baruungoyot formations of Mongolia. These dinosaur parallels may indicate a faunal interchange between the two regions during the end of the Late Cretaceous, from the late Campanian–early Maastrichtian. While absolute dates have yet to be determined for the Zhengyang Formation, it was likely deposited during this time.